income tax, levy imposed on individuals (or family units) and corporations. Individual income tax is computed on the basis of income received. It is usually classified as a direct tax because the burden is presumably on the individuals who pay it. Corporate income tax is imposed on net profits, computed as the excess of receipts over allowable costs.

As an instrument of national policy, the individual income tax has played different roles in different countries at different times, beginning in Great Britain at the close of the 18th century. By 1914 the “personal” income tax had come to be regarded in a number of countries not only as an important revenue instrument but also as an instrument for achieving social reform through income redistribution. Finally, in most countries it has been used to redirect economic decisions through preferential treatment of various activities. It can also act as a stabilizer against economic fluctuations because its effect on purchasing power varies inversely with changes in income and employment. For example, a person who experiences a reduction of income due to a job loss will typically owe less in taxes; the employed person will pay more in taxes but will have more income available for purchases. More recently, however, opinion has shifted away from the view that the income tax should be used for these purposes because of the costs involved, in terms of disincentives and other distortions of economic behaviour.

Regarding income taxes on corporations, nearly all countries assess them, but the provisions and rates differ widely. Since industrialized countries generally have larger corporate sectors than less-developed countries, corporation income taxes in developed countries tend to be greater in relation to national income and total government revenue—except in major mineral-producing areas of less-developed countries.

The United Kingdom for a long time applied the income tax on corporations (companies) purely as a supplement to the taxation of individuals. Shareholders had to pay tax on dividend income only to the extent that the rate of individual tax applicable to such income exceeded the corporate rate; they received refunds if that rate was less than the corporate rate. This system was modified in 1937 and replaced in 1965 by a separate corporation tax.

In the United States the federal corporation income tax, adopted in 1909, predates the modern individual income tax (authorized by constitutional amendment in 1913). Before World War II the corporate tax usually yielded more revenue than the individual income tax, but this had changed by the beginning of the 21st century, when the individual income tax produced about five times more revenue than did the corporate tax. About three-fourths of U.S. states levy taxes on corporations.

Rationale for taxation

Acceptance of income taxation as the fairest kind of tax is based on the premise that an individual’s income is the best single index of one’s ability to contribute to the support of government. Moreover, compared with sales taxes or property taxes, an income tax is easier to change when the taxpayer’s ability to pay taxes is affected by various life-course circumstances (such as the number of dependents the taxpayer supports or extraordinary medical expenses).

Another argument for income taxation proceeds from its relation to a nation’s economic performance. Compared with the amounts produced by sales taxes or wealth taxes, the receipts from the individual income tax tend to rise more steeply in economic booms and drop more sharply in recessions. This occurs in part because individual income itself is quite sensitive to changes in the level of overall economic activity. In addition, income taxation is regulated by a progressive rate structure (which can be thought to include the personal exemption as a zero tax rate). As a result, a rise in individual income creates additional income that is taxed at a higher rate. Conversely, a drop in individual income causes some taxpayers to be taxed at lower bracket rates. Because of this, taxpayers’ tax liabilities fluctuate more than their incomes—the individual income tax actually offsets some effects of expansionary and contractionary forces during business cycles. Exceptions to a tax code—such as deductions, the indexation of exemptions, and the measurement of income from capital for inflation—reduce the potential for stabilization. (See progressive tax; regressive tax.)

The individual income tax reduces the amount of income individuals have available to spend, save, or invest. Of course, any tax has this result. The question is whether other taxes may achieve the same end more efficiently or with fewer undesirable side effects. It has been argued that a tax on income discriminates against saving and is less favourable to economic growth than a tax on spending because an income tax is levied on all income—even that which is saved and made available for investment—while a consumption tax is not levied on moneys that are put into savings. On the other hand, an income tax does not distort consumer spending patterns the way that selective excise taxes tend to (causing buyers to shift from taxed to untaxed items). The income tax does, however, contain distortions and inequities of its own.

It is difficult to determine the extent to which an income tax reduces the incentive to work. To the extent that the tax reduces total income after taxes, it may lead some persons to work longer in an effort to maintain an established standard of living (the income effect). To the extent that the tax reduces the reward for an extra hour’s work, it may make the taxpayer decide to work less and to indulge in more leisure (the substitution effect); presumably, the larger the income and the more steeply progressive the tax, the greater this substitution effect will be. Finally, a progressive income tax is sometimes said to have an adverse effect on investment, especially in the case of risky ventures, but this has been shown to depend on the provisions a tax law makes for allowing investors to write off their losses.

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